1. Field of the Invention
The present invention generally relates to a tin-plated product. More specifically, the invention relates to a tin-plated product used as the material of an insertable connecting terminal or the like.
2. Description of the Prior Art
As conventional materials of insertable connecting terminals, there are used tin-plated products wherein a tin coating layer is formed as the outermost layer of a conductive material, such as copper or a copper alloy. In particular, tin-plated products have a small deterioration of contact resistance with age, and are used as the materials of connecting terminals for automotive vehicles and so forth which are used in a great environmental load.
However, there is a problem in that tin-plated products can not be used as insertable connecting terminals for a long time since they are soft and easy to wear. In order to eliminate this problem, it is proposed that a coating of a composite material, which contains wear resistant or lubricating solid particles in a metal matrix containing tin as a principal component, is formed on a conductive substrate by electroplating to improve the mechanical wear resistance of a tin-plated product (see, e.g., Japanese Patent Laid-Open Nos. 54-45634, 53-11131 and 63-145819), and there is proposed a connecting terminal to which such a composite coating is applied (see, e.g., Japanese Patent Unexamined Publication No. 2001-526734 (National Publication of Translated Version of PCT/US96/19768). It is also proposed that a coating containing tin or tin/lead and graphite dispersed therein is formed on a conductive substrate to form a conductive coating having an excellent wear resistance (see, e.g., Japanese Patent Laid-Open No. 61-227196).
However, there is a problem in that the conventional tin-plated products produced by the above described methods have a relatively high coefficient of friction although they have an excellent wear resistance. Therefore, if such a tin-plated product is used as the material of an insertable connecting terminal, there is a problem in that the inserting force applied thereto increases